(i) Field of the Invention
The present invention relates to the field of ship and yacht building. Its subject matter is more particularly a method for caulking the deck of ships.
(ii) Description of the Related Art
It has long been known in the art of shipbuilding to use tropical wood species, such as teak, for their extraordinary resistance to wind and weather. Teak, for example, guarantees anti slip properties of the deck of the ship under dry as well as wet conditions. It also provides a protection of the subdeck underneath against weather influences, resulting therefore in a durable deck surface. Further for yacht building, tropical wood species (such as teak) used to cover the deck, are particularly appreciated by the yacht owners for their nice golden-brown colour which appears from light to dark tones.
Construction of a teak deck first requires the bonding of teak boards (also called planks, or strokes or lathes) on the substrate (or ship subdeck) which may be made of a metal (for instance aluminium), of a metallic alloy (such as steel or painted steel), of a material comprising polyester (such as reinforced polyester) or wood (such as plywood). These teak planks may have for instance a parallelepipedic shape, with a length comprised between 10 cm to 5 meters, a width comprised between 3 to 20 cm, and a thickness comprised between 4 mm to 4 cm. By the term “teak plank”, it is also intended to include plywood on which a layer of teak of a few millimetres thick is applied. Teak planks may also be available under various other shapes, depending on the particular geometry of the part of the ship deck. They are generally supplied in different cross-section types, such as a rectangular cross-section, or with a T-profile or a L-profile.
After bonding the teak planks on the subdeck, there remains, between adjacent planks, an empty interspace (also called a seam), which has substantially the shape of a ribbon with a width comprised between 3 to 20 mm (preferably between 5 to 10 mm) and with a depth comprised between 6 to 10 mm. The seam is most of the time a straight ribbon parallel to each side of the rectangular teak planks. In the case of teak planks having a shape other than parallelepipedic, the seam follows the perimeter of such planks, not being necessarily a straight ribbon.
The caulking process comprises sealing (or jointing) the bonded teak planks by filling the seams around them through the application of a sealing composition, for instance a moisture curable sealing composition, in order to obtain, after curing, a joint which prevents dust, dirt, moisture, chemicals or sea water from penetrating into the seam and from being in contact with the subdeck, in order to prevent possible damage or corrosion of the ship deck or subdeck.
The cured sealing composition should possess a hardness appropriate for its use as a joint for of a ship deck.
The cured sealing composition should also confer some movement capability to the joint, resulting in its ability to keep its protective function in case of relative movements of the teak planks, such as shrinking and expanding, due to the changing thermal and environmental conditions. Such ability is linked to some elastic (or rubber-like) behaviour of the cured composition, expressing itself in appropriate tensile stress/strain properties.
Further, it is required of the cured sealing composition that during the relative movements of the teak planks hereinabove mentioned, cohesion of the joint is maintained together with its adhesion to the sides of the teak planks, within the seam. Therefore an appropriate balance of adhesion and cohesion is also required.
This sealing composition (or sealant) is usually applied into the seam directly from its container, namely a cartridge or a flexible package (also called a sausage) whose nozzle has been cut to correspond to the width of the seam. A rope of the sealing composition is so applied within the seam, with a 10% to 20% weight surplus, which is pressed into the seam with a spatula. The ability of the sealing composition to be delivered from the cartridge or sausage in which it is contained, and to fill the seam is reflected in particular by appropriate rheological properties (viscosity).
Immediately after applying the moisture curable sealing composition, a spatula is used to press it into the seams, and to remove excess of it. This operation leaves a thin layer of the moisture curable sealing composition on the surface of the adjacent planks, on either side of the seams. Then the deck is allowed to stay during a certain period of time, depending upon the temperature and relative humidity (usually between 4 to 7 days), so that the moisture curable sealing composition is sufficiently cured.
Thereafter, the ship deck is generally sanded in order to obtain the desired aesthetic appearance of the teak planks, and also to eliminate the part of the cured sealing composition still present as a thin layer on the surface of the adjacent planks, on either side of the seams. Hardness of the sealed composition must be such that the joint is not altered by the carefully carried out sanding operation.
Commercial moisture curable sealing compositions intended for use for deck caulking are known. In particular a moisture curable sealing composition comprising a silyl-modified polyether, more precisely a silyl-modified polypropylene oxide wherein the polypropylene oxide main chain is linked at each of its both ends to a —Si(CH3)(OCH3)2 group through a —CH2—CH2-radical, is marketed by the company Bostik under the name of SIMSON® MSR DC. The silyl-modified polyether polymer comprised in this composition is for instance marketed under the name MS-Polymer® by the Kaneka company. During curing of said moisture curable sealing composition, the silicon-containing end-groups are capable of hydrolysing in the presence of the air moisture and under the influence of a catalyst, to form siloxane linkages. The resulting cured composition possesses the properties required for a teak plank joint.
There is a need however to improve the properties of existing sealing compositions intended for use for deck caulking, in particular with respect to chemical and weathering resistance.
With respect to chemical resistance, there is a growing trend from yacht owners to frequently use cleaning solutions (or brighteners) comprising various chemicals selected from organic or inorganic compounds, with an acidic, neutral, or alkaline nature, in order to clean the teak decks of their yachts and maintain the aesthetic appeal of teak. After long periods of time, as the ship becomes older, there is the problem that the exposure of the ship deck to sea-water, to changing temperature conditions, and to extended exposure to UV-light, in combination with the frequent application of the cleaning solutions on the teak deck, may result in the joint becoming sticky or tacky. In the worst case, the sealant can show staining effects.
In some cases, the cured sealing composition may lose adhesion from the sides of the seams surrounding the teak planks, with the adverse consequence that the subdeck may be in contact with the sea water, resulting in a risk of damage and corrosion of the deck itself or the subdeck.